The invention relates to optical pickup devices and composite optical devices especially suitable for use in an optical disc system.
Along with the recent diversification of optical disc systems, there has been an increase in incompatible optical discs using what are referred to herein as different read/write formats (or simply formats) (for example, CD, CD-R, MD, MO, Phase Change Disc DVD, and so on). These read/write formats can very, e.g., by using laser light from a semiconductor laser for emitting light in the band of 780 nm, laser light from an emitting semiconductor laser for emitting red light in the band of 635 nm (or 650 nm), laser light from a semiconductor laser for emitting blue light, and so forth. The optical pickup devices used to read from and write to these different optical recording media then have what are referred to herein as different read/write specifications.
In order to use a common optical disc system to record and reproduce signals wit different kinds of optical discs having different formats, a system needs different optical pickup devices for respective optical discs having different read/write formats.
On the other hand, considering the large differences in purpose and characteristics between writing semiconductor lasers and reading semiconductor lasers, it would be easier for making an optical pickup device, in some applications, to use a semiconductor laser only for writing and another semiconductor laser for reading.
However, the use of different optical pickup devices for respective optical discs of different formats invites an increase in the dimensions and cost of the optical disc system. Especially when a packaged writing semiconductor laser and a packaged reading semiconductor laser are used to make up an optical pickup device, the optical pickup device itself, and an optical disc system using it, become more bulky. At the same time, these semiconductor lasers and photodetector elements are difficult to assemble because adjustment of their optical axes is more difficult than conventional devices.